Conventionally, touch panels which each simultaneously detect a touch position and a push amount (pressing force) of a touch when an operator touches an operation surface of a planar shape by a finger or the like have been proposed.
For example, Patent Document 1 discloses a thin touch panel which simultaneously detects a touch position and a push amount by disposing capacitance detection electrodes on at least one of a side of a first principal surface and a side of a second principal surface of a piezoelectric film opposing to each other, and disposing piezoelectric voltage detection electrodes at the side of the first principal surface and the side of the second principal surface of this piezoelectric film. An operation surface is at the side of the first principal surface.
Further, Patent Document 2 discloses a thin touch panel which simultaneously detects a touch position and a push amount by disposing capacitance detection electrodes at a side of a first principal surface and a side of a second principal surface of a dielectric film opposing to each other, disposing piezoelectric voltage detection electrodes at a side of a third principal surface and a side of a fourth principal surface of a piezoelectric film opposing to each other, and overlaying the dielectric film and the piezoelectric film while making the second principal surface and the third principal surface oppose to each other. An operation surface is at the side of the first principal surface.
According to Patent Documents 1 and 2, the piezoelectric films are used which are formed by using uniaxially extended poly-L-lactic acid (PLLA). These piezoelectric films (PLLA films) produce voltages in a film thickness direction when being applied a compressing or stretching force in a direction of 45 degrees with respect to a molecular orientation direction (stretching direction).
Patent Document 1: International Publication No. WO2013/021835
Patent Document 2: International Publication No. WO2014/045847